Published German patent application 3,112,229 discloses a start-assist device on a membrane carburetor. Vapor bubbles form in the carburetor when an engine is at standstill. The start-assist device disclosed in this publication is intended to prevent such vapor bubbles from hindering a start-up of the engine in a next start attempt. The membrane carburetor includes an intake channel and a throttle flap disposed in the intake channel as well as a control chamber which is delimited by the membrane and filled with fuel. The metering of fuel into the control chamber is controlled by means of a control valve. The fuel reaches the nozzles from the control chamber and enters the intake channel via the nozzles. A pneumatic actuating element is furthermore provided and has a work chamber which can be charged with the pressure or underpressure in the intake pipe of the engine. The movable partition wall delimits the work chamber and is operatively connected to a valve in the other chamber. This valve is closed when there is an underpressure in the intake pipe. A connecting channel is provided between the control chamber and the additional chamber of the pneumatic actuating element. Via this connecting channel, vapor bubbles or air in the fuel system can flow away when the engine is at standstill.